Tandem telephone system



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Filed Dec. 5 1, 1940 May 5, 1942. `w. B. sTRlcKLER TANDmv TELEPHONE SYSTEM Filed Dec. 3l, 1940 17 Sheets-Sheet 17 l/Vl/E/V TOR W B. STR/CKLER A TTORNEV Patented May 5, 1942 TANDEM-.TELEPHONE'SYSTEM :Vtfaltei' B.' 'Stricklen East Orange,VV N. J., assigner f to Bell Telephone .Laboratories, .Incorporated, New IYorkgN. Y., a corporation of New York 'Application December 31, 1940, SerialiNo. 372,580

(Clflg-i-Z?) 13 Glaims.

This invention relates to telephone-systems and has for its object to. facilitate the establishment of connections between subscribers in oiiices Within exchange areas.

Oiiices within an exchange area may be connected either by direct trunks or .by trunks extending :through av tandem cnice. .'.Whether .direct trunks or tandem trunks are provided for use in a particular connection is `primarily a question of trame density, 'although tandem trunking may also serve to supplement direct trunking.

When two oiices are connected through atandem oice, the resulting connection may or may not exceed the length over which the .terminating equipment may be controlled, andthat .length also depends on the nature of the terminating equipment. 4

In accordance with the presentV invention, means is provided, controlled,bythe-natureof the terminating omce, to determine whetherthe line' designation shall vberecorded. in ,the tandem sender orpassed through the tandem sender to the terminating oiiice.

In case of trouble, the tandem sender. rst tries to route the call to a special trunk in order to cause the originating sender or operator to take over the signaling ofthe. calling subscriber. If this fails the tandem sender itself transmits the signals to the originating office.

Means is also vprovided whereby, .when the terminating office fails. to exert thenecessary control of the connection, thatcontrol is supplied at the tandem sender.

In particular, if noassignment is: received from a terminating. call. indicator oice .the tandem cnice supplies .an articial assignment` and inthe originating sender fails .-.to provideV .the .necessary reverse battery pulse.. the. .tandem sender is equipped to. provide such a pulse.

These and other features ofthe invention will be more clearly understood from a consideration of-.the followingdescriptionin connection with the accompanying drawings. in which:

Fig. 1 shows indiagrammatic form, equipment at an originating office aswellas an incoming trunk at a tandem office;

Fig. 2 shows switches connecting with trunks to a plurality ofterminating offices,v and, schematically, a sender connector, an .cnice linkcon- V nector, a marker and av marker connector;

Figs. 3 to 17 show the tandem sender of which: Fig. 3 shows the counting relays and the ksteering relays;

Figs. 4, 5, B and 10 show the. crossbar register;

Figs. 6 and 7 show the relays for supervising a call indicator call;

Figs. 8 and 13 showthe circuits. for contro-lling a full selector call;

the subscriber `scribe'r or originatingl .then dialsthe designationoftthe Wanted--line,

Fig. llshows the senderfr'elease relays; Figs. 12,' L15 and- 16` show'ttheztroubletirning circuits;

Figs. 14zand'i17 show thecircuits for receiving designations.. and

Fig. 18 shows .the .manner ofiarrangingiiigs. 1 to 1'7, inclusive.

No details of thegoriginating and terminating oi'ices havebeen shown.' Reference is'here made to U.. S. Patent No. 2,235,803, grantedMarchilS, 194,1, to WJW; Carpenter, for acompleteshowing of the originating circuits'at. acrossebarlloiiice, toiPatent No.'2;089,921," grantedAugust 10, 1937, to W.A W. Carpenter for Terminating cross-bar circuits, to 'Patent`No. 1,658,829; granted` February 14, 1928, toC. I-I. Berry for Panel'automatic equipment having access tocalled lines, andto Pat-ent No. 1,968,420, grantedlJuly"31,1934,,to A. C. Powell lfor, Callindicator'equipment iat a manual oiiice.

`rIn the establishmentoi a telephone. connection through atandemy oince' the-connection is extended `from ,the calling-subscriber to'the tandem oliiceunder the control of' an originatingsender and marker.

An oice brush and an oiice group registration is then `transmitted by. means of revertive pulses to the tandem sender, which calls in a tandemA markerand transfers these registrations to the marker. VThe marker selects a. trunk outgoing to the wanted ,cnice and transmits. an indication to the sender of the nature of the terminating oice. i For a full selector oiiicethe tandem sender receivesr thel numerical designationand retransmits it tocontrol the-terminating equipment. to select the wantedline. YFor a call .indicatorjofnce, the'incoming :and .outgoing .trunk conductors are-connected togetherfinxthe sender. .and the designation i is transmitted directly. :g from 1 ,the originating to the terminating oice, the tandem y.sender receiving 1an indicationl when 'the vtransfer is completed 'Whenpthe' designationghas been received at the terminating 'ofi'icev the senderr causes the incoming and outgoing .trunkconductors to be connected togetherby. the.. trunk equipment and the'sender Considering releases.

the` invention in more detail, when at substation IBD originates a call for a subscriber at an oiiicezwhich is reached by way of the .tandem oince, substation H00 is connected by line switches fl and IGZ to adistrict junctor which is in turn connected over sender link switches. |03. and HM with aV subsender. .The subscriber whereupon the sender connects with a decoder marker through the marker connector and .the marker connects with the district junctor.. The sender transmits the oiiice -.designationl tothe marken. which..Y trans1ates:,.the. :designation-.cinto the necessary information for selecting an outgoing trunk to the wanted oiiice, in this case a tandem oiiice, and transmits to the sender instructions as to the manner in which the line designation is to be transmitted to the terminating oce. switches to |08 are operated to connect the district junctor with the trunk, and the marker and marker connector are released. The subscriber sender closes a bridge across the-.tip and ring conductors of the trunk to inform the distant oii'ice that it is ready to proceed.

At the incoming trunk in the tandem oilce the tip of the trunk |09 extends over the tip contact of jack |I0, contacts I `and 2 of relay III, right winding of relay I I8 in parallel withcontact I0 of relay II5 and resistance I|6 to battery through resistance lamp II1. The ring conductor of trunk |09 extends over the ring contact of jack IIO, contacts 1 and 6 of relay |I| to ground at contact I of relay II5. A branch of this circuit extends to the left winding of relay I I8 `but is incomplete with relay II5 normal. The originating sender completes its trunk test operation and then closes a lower resistance bridge ready for oice brush selection. l

Relay I I8 operates over the circuit above traced and this selection loop at the originating ofce, and connects ground over contact 4 of relay I|5 to conductor thereby causing the sender link control circuit to select an idle tandem sender and operate sender link switches 208 and 209 to connect the trunk with the sender.

During the operation of the link circuit, trunk group relay 2I0 is operated, grounding conductors 22|, 222 and 223. At the same time, conductor 224 is grounded, operating relay H00 which extends its operating ground over contact I of relay H09 to the winding of relay IIOI `and battery.`

The grounding of conductors 222 and 223 identies the frame on which the incoming junctor is located. Ground on conductor 222 is connected, over contact 3 of relay |I00 to the winding of relay |500 which in turn connects its operating ground to conductor |5I8 to serve as a locking ground until relay 603 operates. Ground on conductor I5 8 extends over the left back contact of relay |60| to the winding of relay |500 and battery. Relay |600 closes a circuit from ground at its outer right contact over conductor |6|1, left contact of relay |I05, to the winding of relay |I04 and battery. Ground on conductor 223 extends over contact 1 of relay IIOI, con-.

ductor III6 through the windings of select magnet 4I5 and marginal relay 920 to battery. In the absence of trouble, relay 920 does not operate but magnet 4|5 operates, preparing the crosspoints in the corresponding level, and extending its operating ground over conductor 420 to the winding of relay |105 and battery. Y

Relay |105 closes a circuit from ground on conductor I 5| 8, over contact 3 of relay I 105, conductor |120, contact 2 and winding of relay I6I| to battery through resistance I6|2. Relay |6I| operates, locking over its contact 3 to ground on conductor |5I8. At the same contact relay I6II prepares a circuit for relay I6I3 from battery through resistance I6I4, butrelay |6|3 is shunted over its own contact I by the operating circuit of relay IBI I. Relay I6I| closes a circuit from battery through the winding of hold magnet 400, back contact of magnet conductor 42|, contact 4 of relay ISI I, contact 4 of relay |6|3 to the windings of relay I1I3. The right winding of After an idle trunk has been seized...

relay I1I3 extends to battery while the circuit through the left winding remains open until relay ||09 is operated.

The grounding of conductor 22| completes a circuit over contact I of relay |I00, winding of relay I |03 to battery to identify the oiiice unit in .which the wanted line is located.

, Winding of relay |105.

With relay II00 operated conductors 225 and 226 are connected together. The link controller circuit responds to this signal and certain other tests by grounding conductor 221, thereby completing a circuit over contact 1 of relay II00, right front contact of relay H04, conductor |||1 to the left winding of relay 603 and battery. Relay 803 connects ground to conductors 6I6 to 620 aswell as to conductor |518. Relay I |03 now locks to conductor 6I6 and relay |500 locks to conductor I5|8. Ground on conductor 6I8 operates a relay in the controller circuit which marks the sender busy and which returns ground over conductor 228 completing ya circuit over contact 9 of relay 603, conductor 62|, contact I of relay I6I I, conductor |6I8, back contact of relay 920, conductor 922, back contact of relay II, conductor I5|9, contact 2 of relay |I03, -contact of relay ||02 to the winding of relay |I09 and battery.

It may be observed that the circuit for operating relay |I09 makes a number of tests since it can only be completed if one and only one of the ofce unit relays I|02 and ||03 is oper-ated. Likewise it cannot be closed if more than one frame units relay is operated as would be indicated by the operation of relay 920. Nor can it be operated if two frame tens relays are operated. The fact that one frame units and one frame tens relay have been operated is shown by the operation of relay IBI I.

Relay H09, when operated, locks to conductor BIS and grounds conductors I I I9 to II25. Ground on conductor I I9 completes a locking circuit for relay over contact II of relay |103 and the back contact of relay I1I3 in parallel, contacts 4 and 1 of relay |105 to battery through the Ground on conductor |25 extends over contact 2 of relay I| I3 to conductor II26, contact 6 and left winding of relay 603 to hold relay 603 operated. Ground also extends from conductor ||26 over contacts 1 and 8 of relay |I09 to conductor 225 to hold the link switches 208 and-209. A further branch of this circuit extends over -contact 8 of relay |I00 to conductor 229 as an indication that the connection between the incoming junctor and the sender is complete and controller may release.

Relays 603 and ||09 also operate several relays which have no function in the normal operation of the senders. For example, ground on conductor I5I8 completes a circuit over contact 6 of relay I I I3 to battery through the winding of relay 6I0. Relay 6I0 in turn closes a circuit from grounded conductor I5I8, front contact of relay 6I0, contact IV of relay 6|4, contact I of relay |202 to battery through the winding of relay |203. Ground on conductor |I24 operates relay I6|5 over contact 3 of relay I6|6. The function of relays 6I0, I 203 and I6I5 will be discussed in connection with calls which encounter trouble or delay.

When relay H09 operates, it opens the circuit of relay I`| 0| and, when the controller circuit releases, the circuit of relay I |00 is opened and that relay releases. The circuits connecting the controller with the sender which extend over contacts of relays H00 and IIO| are common to a lextends tip conductor 234' over .234 and 235, thef-outgoingtip. and' ring conductors 20|`V and'f232tand control conductors-230,233 and 230,I 'by-means. of linlrl switches" 208 rand i209,

'while' conductorV 225 extends 'to the hold magnetsofzthe-link'switches-as above described. l When relay |100 grounds conductor ||2I vthe 'circuit previously .tracedforf hold magnet 400i of the register switch' is\extended,1in'fparallel with battery through the 'right winding of` relay J |1I3,`

through the left Windingl of relay Il`||3 to ground on conductor II2I. .Relay I 'II3' being dierentlal "does notro-perate at this time,` .but magnet-400 does. operate.: locking over. its inner contactl to grounded conductor I 5w.` With select' magnet.

#I5 operated, the opera-tion o'f'hold `magnet 400 closes cross-point 422. Thelocking' groundvfor magnet 400 A.extends back over the operating circuit of magnet'400 to the right Winding of relay 'I|3, permitting that relay rto operate. Relay I'|I3 opens one branch of the" locking circuit of relay'v |105.

'When the-switches .208 andA 209 have operated, the-trunk tipi and:ring-conductors I34'and |35 are connected through the'link 'tolconductors'234 and235-respectiyely.' The operation/of relay 603 Contact of relay 003. contact I of' relayi604, leftcontact of relay 4lill'ccontact 5| of lrelay102,"contacts 2"and lof relay 601, contact I ofi* relay 100,"contact 2 ofI relay '|02,`back contact of relay 'll I, conductor '|I4., contacts 2.and Sioff relay v1002,conductor IBIS. contact E of relay |'5|4,` contact I of' relay |000; conducta-.|020 to the-Winding of-relay' |102 land battery. .In parallel with .relay |102, condoctor |020 extends to' battery through resistance I` and over contact 'I of relay |5|4, conductor I52I, contact `I of relay resistance I 701.

Ring conductor 235 is also extended over contact I0 of relay 603,.contact `5 of relay 604,right contact of relay 606, Contact? of' relay 102, contacts 'I and 8 of relai/'001, contact I0 of relay 100,'

|105 to battery through contact B of. relay 302, conductor 'I|5, left contact of relay |504, right contact ofrrelay |60I, conductor' ItI to; ground@ through. the winding of 'steppingrelay Ii |2. Relay I'I l2 i'svshunted by ground over contact 8 of relay I-l05,.contac`t 5 yof relay |106 and contact 9 of relay |103.

When relay |100 grounds conductor H22 it completes a circuit over contact 4 of relay 6| I, conductorv 230, through the linkfswitches 209 and y 200 to conductor |30.; operating relayV I I'I. Relay disconnects battery'and ground' through the windings of relay IIB from conductors |34 and '|35 to improvethe pulsing condition'between the subscriber sender and the tandem sender.

Relay |102 operates n-the circuit above traced and closes a circuit vfrom ground'at its front contact, conductor ITIS, contact of relayV I5I`4, conductor I 520, contact I2 ofv relay; I'|03,'contact 2 of relay |105, Winding of relay |706 and battery. RelayIIG locks toconductor |520, .disconnects battery through resistance. |101 -from in shuntA of relay H02 and closes alcircuit for relay '|'|03.

Relay |103 at its contact I2 opens the locking circuitfor relay |105 and magnet 4| 5 .permitting them to release. yWith relays |703 and |7106 "operated and relay |105 released, the shunts around the Awinding 'ofV relay II I2.1are'.-opened. andvthat `relay-l operates.

.Relayf I I I2; in'4 operating; 'closes aszcircultr from ground overY the topcontact 'of :cross-point! T422, conductor 423, contact of relay III2, conductor |`I I8,` inner. upper ccntactof cross-'point' 422, conover" that contact" is 'reversed underrthe control of theframenregister: crossepoints' for approximately half of the calls, since, forodd-numbered frames; conductorjdEB is groundedandf conductors HI8 andl connected over the cross-point,`

While for even-numbered frames, conductor |||8 is Igrounded and nconductors -423 and' 424 :connected together.

When relay-|5|0 operates in responseto the operationof relay III2, itvconnectsfground to conductor |620, holding relay |702 operatedv and shunting both: relay I I I2 and the 'stepping relay of the'. subscribersender. 1 Relay I2 releases, opening the .circuit of relay |5|0 which removes the shunt from relay III2. Relay II|2 reoperates and reoperates'relay |5|0. This. cycle continues until thesubscriber sender, havingcounted a number of releases of its stepping relay determined by the setting of the register thereat, opens the pulsing circuit to release both relay` II I2 and relayl'l02 to terminatethe transmission ofA the i registration.

Each time that 'relay `|5|0 :operates'it `also `closes a circuit from ground atits outer contact,

tery; Relay |10 Si, locksthrough 'the right .Winding 40 "contact of relay |109 to :ground at contact. 4 of relayeI'IUS and contact 8 ofrrelay |103.' 'Relay |108 does not operate in this locking circuit,

of relay |108, back contact; ofwrelay' I`||41,1outer being shunted by the operating circuit of |109. When relay |5l0releases, relay ates.

relay |103 oper- The next grounding of conductor .|522

completes a circuit over lthe left` front contact and left Winding of lrelay |108, lright Winding of relay|`|| 4 and battery.` Relay |'II4 vopens the locking circuit of relays.v |109fand I '|08. Relay releases, but-relay |708 remains'. operated `in series with relay I`I|4 until relay |5| 0 removes ground from comluctor4 |522,` at vwhich timereylays-.|108 and. III4release, leaving the-*three I`|I4 normal, as at the relays |100-, |l09`and 4beginnngof the rst pulse. This lcycle is`re peated as longas relay |5|0 continues to operate andrelease. Thefrightcontact of relay |108 is grounded over contacts 8 and 'lV of relay 4703. Therefore, Withrelay- |108- operated at'the end of odd pulses, conductor I 'Ill' is grounded and wth'relay I'I00'released at therendv ofeven pulses 4conductor |`||6 is grounded.

" The rst connection "of ground" to conductor ll'If'Icompletes'a circuit over. contact Bcf 'relay I 404,.contact of relay I 402, Contact I of relay I 403,: contact I of relayslllll tothe winding of relay |40! and battery. Relay |40! locks over normal contacts ofrelays |002', 4403,4404 and l I 405,-condu'ctor |401 overl contact I 0' of' relay |703 to'grounded conductorl I l i9 ad over contact 5 of. relay :|705 to lgrounded conductorv II2I. On the second pulse, ground on conductor |`I I6 l:extends over contact 4 of rel'ay' 1|40|-to the Wind- '.ingiof'relay |402 and battery.` VRelayld'll? 'locks 

